The Danish government refused to say who kidnapped him or why he had been released, but Daniel Rye Ottosen is coming home. The 25-year-old photographer had been detained in Syria for 13 months, his captivity kept secret for security reasons.

The Associated Press reports that Rye Ottosen had been held since May 2013 after traveling to Syria to chronicle that nation’s ongoing civil war. Danish officials said he was freed on Thursday and was in good health, but little else. “Generally speaking I can say that as government representatives, we never ever have contacts with abductors or any other criminals,” Foreign Minister Egberg Mikkelsen told the Associated Press, declining to name any suspects or groups in the kidnapping. The Danish government also confirmed that national media were aware of his capture but did not report it for security reasons.

Spanish newspaper ABC reports that Danish authorities have made clear they would provide no additional information on the matter. They are also reporting that some Danish news sources have run unofficial details on Rye Ottosen’s capture: namely, that he was kidnapped by radical jihadist terrorists affiliated with Islamic State of Iraq and al-Sham (ISIS) and that the government paid a ransom to bring him home.

A report on Denmark’s TV2 details Rye Ottosen’s career, noting that his professional life had led him to other extremely dangerous territory, particularly Somalia, and that his colleagues believed him prepared for the mission. According to photographer Jan Grarup, who worked with Rye Ottosen, the latter researched extensively for the trip and was not “out there to show the world how tough he is.” The report also notes the circumstances under which he was kidnapped– stopped on a patrol with a guide and an interpreter, Rye Ottosen was the only one in his group not immediately released. It was “probably” ISIS, reads the report.

The ISIS terrorist group has seen its reputation globally balloon in recent weeks due to advances in Iraq, where ISIS soldiers have captured major cities like Mosul and Tikrit and threaten to reach Baghdad. ISIS already has a significant presence on its other warfront, Syria, though the civil war has attracted a number of both non-jihadist anti-Assad opposition and other jihadist groups beside ISIS.